1. Field of the Invention
The present invention relates to a process for regenerating a deactivated catalyst. More particularly, it pertains to a process for efficiently regenerating a deactivated catalyst comprising a zeolite and a noble metal of the group VIII of the Periodic Table supported thereon, especially the catalyst for the production of aromatic compounds.
2. Description of Related Art
It has heretofore been known that a variety of catalysts such as a zeolite with a noble metal of the group VIII of the Periodic Table exemplified by platinum supported thereon are effective for the production of aromatic compounds. However, these catalysts are deactivated by the accumulation of coke on the noble metal during a long-term reaction and no longer function satisfactorily as catalyst, thereby necessitating regeneration of themselves at an appropriate interval. It is familiar to one with ordinary skill in the art that the coke accumulated on a deactivated catalyst such as platinum supported on L-type zeolite can be removed by heating it to a temperature in the range of 430.degree. to 540.degree. C. in the presence of diluted oxygen. Nevertheless, this decoking of the catalyst at such a high temperature brings about the growth of the supported noble metal particles, that is, a decrease in the surface area of the particles, thereby resulting in a decrease in the catalytic activity. It is necessary, therefore, that after the high temperature decoking the catalyst be brought into contact with air with chlorine or a chlorine compound such as carbon tetrachloride at an elevated temperature (oxychlorination treatment) to redisperse the noble metal particles (refer to Japanese Patent Application Laid-Open No. 168540/1985 and Japanese Patent Publication No. 24585/1990).
However, it is extremely difficult to regenerate a catalyst poisoned with sulfur or a heavily deactivated catalyst even by the above-mentioned oxychlorination treatment.
There is also disclosed a process for regenerating a deactivate catalyst comprising the steps of decoking a deactivated catalyst under an oxidative condition; washing it with a neutral or an acidic solution; treating it with an aqueous basic solution; washing it with deionized water; drying it and calcining (International Patent Publication No. 500710/1987). However, the aforesaid process is poor in regeneration efficiency, entails too many steps and requires aqueous solution at least 10 times the catalyst volume.
There are further disclosed a technique by regenerating a deactivated catalyst only by hydrogen reduction treatment (Japanese Patent Application Laid-Open No. 24316/1982) and a technique by regenerating a deactivated catalyst by decoking the same in the presence of a halogen-containing compound (Japanese Patent Application Laid-Open No. 231944/1989). Nevertheless, the regenerated catalyst in the former is inferior in catalytic performance, whereas the regeneration process in the latter suffers the disadvantages that the decoking at a high temperature in the presence of a halogen-containing compound leads to expensive treatment equipment and a hydrochlorofluorocarbon gas used therein as the above compound will unfavorably cause environmental destruction which has become a serious problem in recent years.
Under such circumstances facing the above-mentioned difficulties, intensive research and investigation were concentrated by the present inventors on the development of a process for regenerating a deactivated catalyst that is capable of overcoming the disadvantages of the aforesaid prior arts, facilitating the regeneration of the catalyst deactivated by coke accumulation or sulfur poison or the heavily deactivated catalyst and thus restoring the catalytic activity thereof to the extent comparable to that of a fresh catalyst.
As a result, it has been found by the present inventors that the above-mentioned problems are overcome and the effective regeneration of a deactivated catalyst is attained by decoking the deactivated catalyst and thereafter treating the same with a solution containing a halogen or a halogen-containing compound. The present invention has been accomplished on the basis of the above-mentioned finding and information.